The short-loop feedback control mechanisms of the pituitary hormones growth hormone (GH), luteinizing hormone (LH) and follicle stimulating hormone (FSH) will be investigated in the laboratory rat and in humans. The nature of the bioaminergic and peptidergic pathways involved in this system will be studied in rats and humans. Studies localizing the site of feedback will be carried out in the rat. The possibilities that the elevated GH levels found in Diabetes Mellitus and Acromegaly and the depressed GH levels found in obesity involve an alteration of the set-point of the feedback loop will be investigated. The possibility that an altered LH and FSH feedback system is the basis of hypogonadotropic hypogonadal states such as weight-loss induced and spontaneous amenorrhea will also be investigated.